Low distortion large swing frequency down coverter filter amplifier circuit

Abstract

A semiconductor integrated circuit to provide a low distortion, large swing intermediate frequency wherein the circuit includes the function of mixing, filtering, and amplification on a single chip. A pair of differential currents are obtained from the mixer, the differential currents are filtered and conditioned, converted to a pair of differential voltages and amplified to obtain the low distortion, large swing intermediate frequency.

What we claim is: 
     
       1. A circuit to provide a low distortion, large swing intermediate frequency, the circuit comprising: a first portion of the circuit which outputs first and second currents each of which include a first frequency component equal to a sum of the frequencies of two sets of signals input to the first portion of the circuit and a second frequency component equal to a difference of the frequencies of the two sets of signals input to the first portion of the circuit;   a second portion of the circuit that receives the first and second currents from the first portion of the circuit and filters one of the first or second frequency components out of the first and second currents; and   a third portion of the circuit which amplifies a remaining frequency component of the first and second currents the remaining frequency component being the first or second frequency component of the first and second currents that was not filtered by the second portion of the circuit.   
     
     
       2. The circuit of claim 1, further comprising a fourth portion of the circuit which conditions the first and second currents. 
     
     
       3. A circuit to provide a low distortion, large swing intermediate frequency, the circuit comprising: a first portion of the circuit which outputs first and second currents each of which include a frequency component equal to a sum of the frequencies of two sets of signals input to the first portion of the circuit and a frequency component equal to a difference of the frequencies of the two sets of signals input to the first portion of the circuit;   a second portion of the circuit which filters one of the two frequency components;   a third portion of the circuit which amplifies a remaining frequency component; and   a fourth portion of the circuit which conditions the first and second currents, said current conditioning circuit comprising first and second current mirrors.   
     
     
       4. The circuit of claim 3, wherein the third portion of the circuit comprises a current-to-voltage amplifier. 
     
     
       5. The circuit of claim 4, wherein the current to-voltage amplifier comprises a differential amplifier and a first and a second transistor. 
     
     
       6. The circuit of claim 5, wherein the first and second transistor in the current-to-voltage amplifier each utilize negative feedback. 
     
     
       7. The circuit of claim 6, wherein the first portion of the circuit comprises: a pair of differential amplifiers connected to a first pair of input terminals wherein the first of the two sets of signals are input; and   a differential amplifier connected to a second pair of input terminals wherein the second of the two sets of signals are input.   
     
     
       8. A circuit to provide a low distortion, large swing intermediate frequency, the circuit comprising: a mixer circuit which outputs a pair of differential currents;   a current-to-voltage amplifier coupled to the mixer circuit to amplify the pair of differential currents;   a filter circuit coupled between the mixer circuit and the current-to-voltage amplifier; and   a current conditioning circuit coupled between the filter circuit and the current-to-voltage amplifier, the current conditioning circuit comprising a pair of current mirrors.   
     
     
       9. The circuit of claim 8, wherein the current-to-voltage amplifier comprises a differential amplifier and a pair of transistors each utilizing negative feedback. 
     
     
       10. A method of obtaining a low distortion, large swing intermediate frequency from a circuit on a single semiconductor integrated chip, the method comprising: obtaining a pair of differential currents having, a first frequency component and a second frequency component;   filtering the second frequency component out of the pair of differential currents leaving a filtered pair of differential currents;   converting the filtered pair of differential currents to a pair of differential voltages; and   amplifying the pair of differential voltages.   
     
     
       11. The method of claim 10, further comprising conditioning the filtered pair of differential currents. 
     
     
       12. The method of claim 11, wherein the pair of differential currents is obtained from mixing two sets of signals.